The present invention relates to a method for. mid-span branching of optical fiber cable network and more specifically to a method for mid-span branching of optical fiber cable which makes the mid-span branching possible without excess length of the optical fiber cable.
In general, optical fiber cables are installed in the networks of loop distribution, star distribution, or other distribution in consideration of economy and reliability of installation, and flexibility to quantitative change of and diversification of service.
By the loop distribution, as shown in FIG. 1A, the excess length of cables for mid-span branching is ensured beforehand in the manholes or on the poles 1, 2, 3, 4, 5, 6 which are, when the cables are initially installed, the anticipated points for branching. When the demand for the cores arises in the middle of service, branch cable is installed from the point of demand for the cores to the point of the loop distribution network for branching. Also, the branched cores of existing main cable in the network are spliced with the branching cores of the branch cable. Thus the network is of the loop-shape.
By the star distribution, as shown in FIG. 1B, the excess length of cables for mid-span branching is ensured beforehand in the manholes or on the poles 1, 2, 3, 4 which are, when the cables are initially installed, the anticipated points for branching. When the demand for the cores arises in the middle of service, branch cable is installed from the point of demand for the cores to the point of the star distribution network for branching. Also, the branched cores of existing main cable in the network are spliced with the branching cores of the branch cable. Thus the network is of the star-shape.
In branching of the optical fiber network described above, there have been provided methods for access-point branching by which branch cable is branched from the network at the point of access to the point of demand for the cores, and for mid-span branching by which branch cable is branched from the network, not at the point of access but at the mid-point of the network cable, to the point of demand for the cores.
In the method for mid-span branching, to avoid tension on the branching part, the excess length of the cables must be ensured for the minimum length of core of the optical fiber cable for the distance from the branching part to branching device, response to demand for re-access in the case of access-failure, malfunction, operational needs, and etc.
Because the prior arts need the excess length of cables as mentioned above, as shown in FIG. 2A, existing main cable 20 is pulled out from the conduit line 10 in the manhole 1 that is the position of mid-span branching, supported by supporter 30, and the slack loop of cable is assumed. Thus the excess length of the cables is ensured. The cores of the existing main cable 20 and the branch cable 40 are placed in the manhole 1.
As shown in FIG. 2B, the excess length of cables is fastened on the prop 31. Branching part 100 is formed by unsheathing predetermined portions of the loop for the cores of the cable to be taken out. Splice closure is installed at the unsheathed part.
In the case where the excess length of cables either can""t be or isn""t ensured in the manhole that is supposed to be the position of mid-span branching, as shown in FIG. 3, branch cable 40 is installed in the manhole 2 adjacent to the manhole 1 which is supposed to be the position of mid-span branching. The splice closure 50 is disjointed and the branch cable 40 is branched from the existing main cable 20, which is the access point branching method. Herein, for the mid-span branching to be completed, at most 500 meters of the branch cable is necessary.
Due to the long excess length of the cable for mid-span branching of prior arts described above, however, there are several problems listed below on usability, workability, and economy in efficient installation of the network.
Firstly, the excess length of cables is generally endured excessively because workers cannot decide exact points of branching when initial installation of the cables. Also, there are the cases when extra branch cables are installed to the access point of the loop/star distribution network because of the lack of the excess length of cables at the points of mid-span branching. Thus, the cost of installation or branching is excessively high.
Secondly, in the case of decision of the incorrect points for branching, ensured excess length of cables must be pulled to the points of mid-span branching or extra branch cables are installed to the points where the excess length of cables has been already endured. Thus the cost for extra installation occurs.
Thirdly, the ensured excess length of cables is of such length that preserved cores are accommodated in the splice closure, which may reduce workability.
Fourthly, unsheathing the slack loop of excess length of the cables takes long time.
Fifthly, the splice closure must have the room for, at least, the allowable radius of curvature of unit of cores with hardened Polybutadien Terephthalate (PBTP), unit of cores having preserved cores. So it is hard to put the unit of cores in order in the splice closure, which reduces reliability of cores of the preserved unit having the cores in operation.
Sixthly, the cables in the manhole cannot be put in order due to the ensured excess length of cables, which may reduce workability. The ensured excess length of cables on the poles also reduces the reliability and a fine view.
It is, therefore, an object of the present invention to provide a method for mid-span branching that provides marginal length of the existing main cable from which the branch cable branches off without the excess length of cables that forms a slack loop.
To accomplish the above object of the present invention, there is provided a method for mid-span branching of optical fiber cable without excess length of cables, comprising the steps of: setting an existing main cable and a branch cable; unsheathing main branched part and sub branched part of the main cable with preserved part formed between the main branched part and the sub branched part; choosing and cutting branched cores with preserved cores remaining uncut at the main branched part, the branched cores having first branched cores and second branched cores; connecting the first branched cores to first branching cores to make temporary connection, first branching cores in the branch cable; pulling out the temporary connection to the sub branched part through the preserved part; and splicing the first branched cores and the first branching cores at the sub branched part, and splicing the second branched cores and second branching cores at the main branching part, second branching cores in the branch cable.
In accordance with another aspect of the present invention, there is provided a method for mid-span branching of optical fiber cable, comprising the steps of: setting an existing main cable and a branch cable; unsheathing main branched part and sub branched part of the main cable with preserved part formed between the main branched part and the sub branched part; choosing and cutting branched cores with preserved cores remaining uncut at the main branched part, the branched cores having first branched cores and second branched cores; pulling out the first branched cores to the sub branched part through the preserved part; setting hollow member above the preserved part; pulling out first branching cores to the sub branched part through the hollow member, first branching cores in the branch cable; and splicing the first branched cores and the first branching cores at the sub branched part and splicing the second branched cores and second branching cores at the main branched part, second branching cores in the branch cable.
Also, in accordance with another aspect of the present invention, there is provided a method for mid-span branching of optical fiber cable, comprising the steps of: setting an existing main cable and a branch cable; unsheathing main branched part and sub branched part of the main cable, preserved part formed between the main branched part and the sub branched part; choosing and cutting branched cores with preserved cores remaining uncut at the main branched part, the branched cores having first branched cores and second branched cores; pulling out the first branched cores to the sub branched part through the preserved part; aligning end of the branch cable with end of the sub branched part; unsheathing main branching part and sub branching part of the branch cable with second preserved part formed between the main branching part and the sub branching part, main branching part and sub branching part of the branch cable corresponding respectively to the main branched part and the sub branched part of the main cable; pulling out second branching cores to the main branching part through the second preserved part, second branching cores in the branch cable; and splicing the first branched cores and first branching cores at the sub branched part and splicing the second branched cores and the second branching cores at the main branched part, first branching cores in the branch cable.